The inventor of this invention has proposed various types of flexible conveyor rail having a part that can freely bend upwardly or downwardly in a conveyor system such as a trolley conveyor system, a cross conveyor system, or a pallet conveyor system. Such flexible conveyor rails are described in Japanese Patent Laid-Open Publication Nos. H3-50061, H4-128403, H4-64602, H4-64603, H4-235811, and H4-23518.
In the flexible conveyor rail shown in the Japanese Patent Laid-Open Publication No. H3-50061, rail pieces made by cutting a lip channel steel into short pieces are used. An example of such a flexible conveyer rail is shown in FIG. 10 in the patent publication and is applied to a trolley conveyor system. The flexible conveyor rail by this prior art has contributed to a relatively highly efficient electrodeposition coating system in which various types of works are transferred.
Further, by incorporating a plurality of flexible conveyor rails such as shown in Japanese Patent Laid-Open Publication No. H4-63297 into the electrodeposition coating system, the flexible conveyer rail in the conventional technology has contributed to improvements in the operation efficiency and labor savings.
In the aforementioned flexible conveyor rails, because each rail piece is produced from a lip channel steel, it is limited to convey relatively light weight works. For example, the maximum transfer capacity of the trolley conveyer is limited to around 75 kg per hanger. In the crossbar conveyor where two conveyer rails are arranged in parallel, the work transfer capacity of up to about 150 kg can be achieved.
Recently, there is increasing demand for transferring a middle weight works. Namely, the work transfer capacity of greater than 150 kg per hanger for a trolley conveyor having a single conveyor rail is desired. Moreover, if possible, the demand extends to transfer heavy weight works, i.e, the transfer capacity of 500-600 kg per hanger.
The inventor of this invention has proposed a flexible conveyor rail having a greater transfer capacity in the Japanese Patent Laid-Open. Publication No. 4-64602 and U.S. Pat. No. 5,101,734. In this flexible conveyor, rail pieces which have been produced by cutting an I-shaped steel into short pieces are used. In each rail piece, a channel piece is fixed to the top of an I-shaped piece. The opposite side plates are fixed to the respective side walls of the channel piece in a manner offset backwardly or forwardly. Each set of the I-shaped piece, the channel piece and the side plates is connected to the other set through connecting plates which are offset relative to the side plates backwardly or forwardly in a predetermined amount. The side plates and the connecting plates are pivotally connected with one another through pivotal bolts to form a flexible conveyor rail. The inventor has conducted various experiment on this flexible conveyor rail.
However, in the flexible conveyor rail described above, the self-weight is very heavy (for example, 1,800 kg to 2,000 kg for the length of 4 m) due to the structure. Moreover, looseness in the conveyor rail is unnecessarily large at the bent portions of the conveyor rail probably because the flexibility for the up-down bending is achieved solely by the construction wherein the end surfaces of adjacent components of the rail pieces contact with one another.
As a result, smooth bending operations in the work transfer tends to be hindered, or the smooth transfer of the works tends to be interfered. Thus, it has become apparent that the flexible conveyor rail using the I-shaped rail pieces and the channel pieces in the conventional technology has a structural problem.
In the flexible conveyor rail based on the rail pieces of lip channel steel type metal shown in the Laid-Open Publication No. H3-50061 described above, two or three hangers can be provided in about four (4) meter length of the flexible conveyer rail stationary or moving along the conveyor rail. However, in the flexible conveyor rail described above, in the Laid-Open Publication No. H4-65602, i.e., U.S. Pat. No. 5,101,734, at most one hanger can be provided in the same four (4) meter length of the conveyor rail because the self-weight is too large.
In such a case, the spacing of the hangers in the backward and forward direction has to be made large, resulting in lessor numbers of works that can be transferred by the transfer system. This requires extra transfer operations, thereby decreasing the operation efficiency and transfer efficiency. Moreover, the transfer system which is needlessly long as a whole must be implemented.